The present invention relates to a laser irradiation device for use in laser processing of ceramics, etc., and a laser processing method performed using the same.
Circuit boards and the like equipped with electronic parts have been produced using a hard and brittle material such as a ceramics material, glass material, silicon material or the like. In order to cut a board formed from such a hard and brittle material, it is necessary to form a groove on the surface of the board, or to form fine holes inside the board. As means for the formation, laser processing has been widely used. In laser processing, a laser beam emitted from a light source is converged using an irradiation optical system such as a lens, and a laser converged spot (beam waist) having an elevated power density is irradiated on the surface or the interior of the board to execute the processing.
At present, in attempts to miniaturize electronic parts and to improve process yield of boards by decreasing the processing site, fine grooves or holes are formed on and/or in the board, and formation of deeper grooves or holes has been demanded. Also, in hole processing, formation of finer holes with a lower degree of tapering has been demanded. In order to realize such demands taking advantages of characteristics of beam waist of a converged laser beam, it is preferable to form a plurality of focal points along an optical axis direction. In addition, characteristics of the beam waist are determined by properties of an irradiation optical system (particularly, light converging lens), which will be used subsequently, based on the wavelength and beam quality of the laser beam.
Methods for forming a plurality of focal points along an optical axis direction of a laser beam include: (A) a method in which a bifocal lens is used to allow the laser beam to be converged at a plurality of focal points (see JP-A No. 2006-192503); (B) a method in which a beam splitter is used to spatially split a laser beam, and a beam divergence angle of one of the split beams is altered and resynthesized, followed by converging on a processed face with a single light converging lens (see JP-A (Japanese translation of PCT international application) No. 2006-525874); (C) a method in which a plurality of times of processing are repeated while mechanically switching a plurality of lenses having different focal lengths (see JP-A No. 2007-290932), and the like.
However, according to the above method (A), a special light converging means such as a lens having a unique shape is needed. Further, the above method (B) involves problems in production and preparation as it is difficult to allow optical axes of synthesized two laser beams to agree with one another, and a reflecting surface having a large curvature radius must be provided. Furthermore, according to the above method (C), there arise problems of impairment of processing efficiency, and deterioration positional accuracy among each of processings, and the like.